The present invention relates generally to interface devices between humans and computers, and more particularly to computer interface devices that provide force feedback to the user.
Virtual reality computer systems provide users with the illusion that they are part of a “virtual” environment. A virtual reality system will typically include a computer processor, such as a personal computer or workstation, specialized virtual reality software, and virtual reality I/O devices such as head mounted displays, sensor gloves, three dimensional (“3D”) pointers, etc.
Virtual reality computer systems can be used for training. In many fields, such as aviation and vehicle and systems operation, virtual reality systems have been used successfully to allow a user to learn from and experience a realistic “virtual” environment. The appeal of using virtual reality computer systems for training relates, in part, to the ability of such systems to allow trainees the luxury of confidently operating in a highly realistic environment and making mistakes without “real world” consequences. For example, a virtual reality computer system can allow a doctor-trainee or other human operator or user to “manipulate” a scalpel or probe within a computer-simulated “body”, and thereby perform medical procedures on a virtual patient. In this instance, the I/O device which is typically a 3D pointer, stylus, or the like is used to represent a surgical instrument such as a scalpel or probe. As the “scalpel” or “probe” moves within a provided space or structure, results of such movement are updated and displayed in a body image displayed on the screen of the computer system so that the operator can gain the experience of performing such a procedure without practicing on an actual human being or a cadaver. In other applications, virtual reality computer systems allow a user to manipulate the controls of complicated and expensive vehicles and machinery for training and/or entertainment purposes. For example, a pilot or astronaut in training can operate a fighter aircraft or spacecraft by manipulating controls such as a control joystick and buttons and view the results of controlling the aircraft on a virtual reality simulation of the aircraft in flight. In yet other applications, a user can manipulate objects and tools in the real world, such as a stylus, and view the results of the manipulation in a virtual reality world with a “virtual stylus” viewed on a screen, in 3-D goggles, etc.
For virtual reality systems to provide a realistic (and therefore effective) experience for the user, sensory feedback and manual interaction should be as natural as possible. Therefore, in addition to sensing and tracking a user's manual activity and feeding such information to the controlling computer to provide a 3D visual representation to the user, a human interface mechanism should also provide force feedback (“haptic” or tactile sensations) to the user. The need for the user to experience realistic force information and sensation is extensive in many kinds of simulation and other applications. For example, in medical/surgical simulations, the “feel” of a probe or scalpel simulator is important as the probe is moved within the simulated body. It would invaluable to a medical trainee to learn through force feedaback how an instrument moves within a body, how much force is required depending on the operation performed, the space available in a body to manipulate an instrument, etc. In simulations of vehicles or equipment, force feedback for controls such as a joystick can be necessary to realistically teach a user the force required to move the joystick when steering in specific situations, such as in a high acceleration environment of an aircraft. In virtual world simulations where the user can manipulate objects, force feedback is necessary to realistically simulate physical objects; for example, if a user touches a pen to a table, the user should feel the impact of the pen on the table. An effective human/computer interface not only acts as an input device for tracking motion, but also as an output device for producing realistic force sensations. A “high bandwidth” interface system, which is an interface that mechanically and electrically allows accurate control over force feedback using fast control signals within a broad range of frequencies, is therefore desirable in these and other applications.
In addition, there is a desire to provide force feedback to users of computer systems in the entertainment industry. Styluses, joysticks, and other interface devices can be used to provide force feedback to a user playing a video game or experiencing a simulation for entertainment or learning purposes. Through such an interface device, a computer system can convey to the user the physical sensation of colliding into a wall, moving through a liquid, driving over a bumpy road, and other sensations. The user can thus experience an entire sensory dimension in the gaming experience that was previously absent. Force feedback interfaces can provide a whole new modality for human-computer interaction.
There are number of devices that are commercially available for interfacing a human with a computer for virtual reality simulations. There are, for example, 2-dimensional input devices such as mice, trackballs, joysticks, and digitizing tablets, as wells as 3-dimensional interface devices. A 3-dimensional human/computer interface tool sold under the trademark Immersion Probe™ is marketed by Immersion Human Interface Corporation of Santa Clara, Calif., and allows manual control in 3-dimensional virtual reality computer environments. A pen-like stylus allows for dexterous 3-dimensional manipulation in six degrees of freedom using a serail configuration of links and joints. The Immersion Probe, however, does not provide force feedback to a user and thus does not allow a user to experience an entire sensory dimension in virtual reality simulations. Prior art force feedback instruments and joysticks provide physical sensations to the user by controlling motors that are coupled to the joystick.
In typical multi-degree of freedom apparatuses that include force feedback, there are several disadvantages. Since actuators which supply force feedback tend to be heavier and larger than sensors, they would provide inertial constraints if added to a device such as the Immersion Probe. In a typical force feedback device, such as Per Force from Cybernet Systems Inc., a serial chain of links and actuators is implemented to achieve multiple degrees of freedom in a desired object positioned at the end of the chain, i.e., each actuator is coupled to the previous actuator. The user who manipulates the object must carry the inertia of all of the subsequent actuators and links except for the first actuator in the chain; which is grounded. For example, the user carries the weight of five ungrounded motors in the Per Force device. Other force feedback devices have a different, non-serial type of linkage, but include several ungrounded motors; for example, the Phantom from Sensable Devices Inc., includes three driven degrees of freedom but only one out of three motors is grounded. The end result is high inertia which corrupts the bandwidth of the system, providing the user with an inaccurate interface. These interfaces also introduce tactile “noise” to the user through friction and compliance in signal transmission and limit the degree of sensitivity conveyed to the user through the actuators of the device.
Other systems, such as a joystick using a slotted bail mechanism, are able to provide two grounded actuators, which enhances the realism of the force feedback experienced by the user. However, these systems are limited in bandwidth by their mechanisms, which tend to be inaccurate and ill-suited for effectively transmitting forces to the user. In other other force feedback interfaces, such as the Impulse Engine from Immersion Corporation, two grounded actuators provide high bandwidth force feedback to a user in two degrees of freedom. However, if it is desired to provide forces in a third degree of freedom, then the user is typically required to carry the weight of the third actuator supplying force in that third degree of freedom, which degrades the realism of the forces felt using the force feedback interface device.
In yet other force feedback interface systems, motors are coupled to a mechanism using cables which transmit forces from the motor to the mechanism. However, in many of these interface systems, the forces from one motor influence the tension on other motors and cables in the system, thus causing additional degradation in the force transmission. In addition, the calculation of forces to provide a desired force sensation to the user can be complicated in such a coupled actuator system, thus decreasing the response time of the system.